Method for signal transmission in wireless systems

ABSTRACT

A method is provided for forming a signal in a wireless communication system in which a plurality of terminals commonly use time and frequency resources for efficient code hopping. The method includes allocating the same frequency-axis sequence and different time-axis sequences to a plurality of terminals by using a resource index according to a first slot in the first slot; and allocating different frequency-axis sequences and different time-axis sequences to the plurality of terminals by using a resource index according to a second slot in the second slot.

PRIORITY

This application is a Continuation of U.S. application Ser. No.12/664,480, which was filed in the U.S. Patent and Trademark Office onDec. 14, 2009, and is a National Phase Entry of PCT InternationalApplication No. PCT/KR08/03396, which was filed on Jun. 16, 2008, andclaims priority to Korean Patent Application Serial No. 10-2007-0058590,which was filed in the Korean Intellectual Property Office on Jun. 14,2007, the entire disclosure of each of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

When a plurality of terminals simultaneously use anacknowledgement/negative acknowledgement (ACK/NACK) channel in awireless communication system, code division multiplexing (CDM) may beused to allow for the plurality of terminals. In CDM, each of theplurality of terminals transmits a signal multiplied by a spreading codeallocated thereto.

The present invention relates to code hopping for efficiently mitigatinginterference among terminals in the same cell and between terminals ofadjacent cells when each of a plurality of terminals uses a spreadingcode along a frequency axis and a spreading code along a time axis.

The present invention is derived from a research project partlysupported by the Information Technology (IT) Research & Development(R&D) program of the Ministry of Information and Communication (MIC) andthe Institute for Information Technology Advancement (IITA)[2005-S-404-13, Development of Radio Transmission Technology for 3GEvolution].

2. Description of the Related Art

The present invention relates to a method of transmitting anacknowledgement/negative acknowledgement (ACK/NACK) signal by a terminalas a response to data received from a base station.

A receiver sends an ACK signal to a transmitter when the receiver issuccessful in demodulating received data, and sends a NACK signal to thetransmitter when the receiver is unsuccessful in demodulating thereceived data. Each of the ACK/NACK signal is expressed as one bit percodeword. A plurality of terminals should be able to simultaneouslytransmit their ACK/NACK signals by using given time and frequencyresources through multiplexing.

Multiplexing techniques are classified into frequency divisionmultiplexing (FDM) and code division multiplexing (CDM). While FDM is aform of multiplexing where a plurality of terminals use different timeand frequency resources, CDM is a form of multiplexing where a pluralityof terminals use the same time/frequency resources but transmit signalsmultiplied by orthogonal codes so as for a receiver to distinguish theplurality of users.

In uplink, a Zadoff-Chu sequence is widely used because it has an idealpeak to average power ratio (PAPR). Such a Zadoff-Chu sequence achievesorthogonality between terminals through cyclic delay without multiplyinga signal by a specific code in a frequency domain.

A terminal transmits an uplink ACK/NACK signal to a base station tosignify successful or unsuccessful receipt of downlink data. The uplinkACK/NACK signal requires one bit per codeword used to transmit thedownlink data.

FIG. 1 illustrates time/frequency resources used by a terminal totransmit an uplink ACK/NACK signal through a control channel in a 3^(rd)generation partnership projection long term evolution (3GPP LTE) system.Referring to FIG. 1, resources used by one control channel are groupedinto two separate resource blocks. Each of the two resource blocksincludes N subcarriers along a frequency axis, and 7 orthogonalfrequency division multiplexing (OFDM) symbols, which corresponds to oneslot, along a time axis. One slot has a length of 0.5 ms.

In FIG. 1, a plurality of terminals may commonly use one controlchannel. That is, one control channel may be shared by the plurality ofterminals.

In this case, in order to distinguish the plurality of terminals usingthe same control channel, a specific code sequence is allocated to eachof the plurality of terminals. That is, each of the plurality ofterminals forms and transmits a signal spread on a frequency axis and atime axis by using its own specific code.

FIG. 2 illustrates a code sequence and a symbol transmitted to each of Nsubcarriers in an ACK/NACK channel occupying a resource block thatincludes the N subcarriers on a frequency axis and 7 OFDM symbols on atime axis. In FIG. 2, the resource block corresponding to one slotdescribed with reference to FIG. 1 occupies N subcarriers on a frequencyaxis and includes 7 symbol blocks BL #0 through #6 on a time axis.

When CDM is used in order to distinguish signals of a plurality ofterminals, a symbol and a sequence may be mapped to each time/frequencyresource as shown in FIG. 2. In order to distinguish the plurality ofterminals, a sequence is applied to each of the frequency axis and thetime axis. In FIG. 2, a reference signal is used for channel estimation,and pre-determined signal is communicated between a terminal and a basestation.

The base station estimates a channel by using a reference signal, anddemodulates an ACK/NACK symbol transmitted by a control signal by usingthe estimated channel. Each time/frequency resource transmits a signalmultiplied by two or three symbols.

That is, a time/frequency resource on which a reference signal istransmitted is obtained by multiplying a frequency-axis sequence symbolC_(q) ^(m)(k) a time-axis sequence symbol R_(i) (i=0, 1, 2). Atime/frequency resource on which a control signal is transmitted isobtained by multiplying a frequency-axis sequence symbol C_(q) ^(m)(k),a time-axis sequence symbol C_(i) (i=0, 1, 2, 3), and an ACK/NACK symbolQ.

In FIG. 2, the frequency-axis sequence symbol C_(q) ^(m)(k) is given byEquation (1).

$\begin{matrix}{{{C_{q}^{m}(k)} = {\exp\lbrack {{\mathbb{i}}\frac{2\pi}{N_{ZC}}{m( \frac{( {k - q} )( {k - q + 1} )}{2} )}} \rbrack}},{k = 0},1,2,\ldots\mspace{14mu},{N - 1}} & (1)\end{matrix}$

In Equation (1), N_(ZC) is the length of a Zadoff-Chu sequence appliedto a k^(th) subcarrier on the frequency axis. The small letter m is aprimary index, and q is a cyclic delay index.

One sequence is applied to each of a reference signal and a controlsignal along the time axis. That is, a sequence applied to a controlsignal in FIG. 2 is expressed as C₀, C₁, C₂, C₃. A sequence applied to areference signal is expressed as R₀, R₁, R₂.

Currently, in 3GPP LTE, three reference signals per slot are used for anuplink ACK/NACK channel.

Also, in order to distinguish terminals, a Zadoff-Chu sequence along afrequency axis is used and a discrete Fourier transformation (DFT)vector, a Walsh-Hadamard sequence, or a Zadoff-Chu sequence along a timeaxis may be used.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention to provide an improvedmethod of forming a signal in a wireless communication system in which aplurality of terminals commonly use time and frequency resources.

In accordance with an aspect of the invention, a method is provided forforming a signal in a wireless communication system in which a pluralityof terminals commonly use time and frequency resources. The methodincludes allocating the same frequency-axis sequence and differenttime-axis sequences to a plurality of terminals by using a resourceindex according to a first slot in the first slot; and allocatingdifferent frequency-axis sequences and different time-axis sequences tothe plurality of terminals by using a resource index according to asecond slot in the second slot.

In accordance with another aspect of the present invention, there isprovided a method of forming a signal in a wireless communication systemin which a plurality of terminals commonly use time and frequencyresources, the method comprising: allocating the same frequency-axissequence and different time-axis sequences to a plurality of terminalsby using a resource index according to a first slot in the first slot;and allocating different frequency-axis sequences to the plurality ofterminals by using a resource index according to a second slot in thesecond slot.

In accordance with another aspect of the present invention, there isprovided a method of forming a signal in a wireless communication systemin which a plurality of terminals commonly use time and frequencyresources, the method comprising: causing one or more terminals, whichuse the same frequency axis code and different time axis codes in afirst slot, to constitute a terminal group for a reference signal symbolblock; causing one or more terminals, which use the same frequency axiscode and different time axis codes in a first slot, to constitute aterminal group for a control signal symbol block, which is independentfrom the terminal group for the reference signal symbol block; causingthe one or more terminals belonging to the same terminal group for thereference signal symbol block in the first slot to belong to differentterminal groups for a reference signal symbol block in a second slot;and causing the one or more terminals belonging to the same terminalgroup for the control signal symbol block in the first slot to belong todifferent terminal groups for a control signal symbol block in a secondslot.

In accordance with another aspect of the present invention, there isprovided a method of forming a signal in a wireless communication systemin which a plurality of terminals commonly use time and frequencyresources, the method comprising: causing one or more terminals, whichuse the same frequency axis code and different time axis codes in afirst symbol block, to constitute one terminal group on one frequencycode; and causing the one terminal group to use a frequency axis code,which is different from the frequency axis code used in the first symbolbock, in a second symbol block different from the first symbol block inone slot.

In accordance with another aspect of the present invention, there isprovided a code hopping method for reducing interference betweenterminals in a wireless communication system in which a plurality ofterminals commonly use time and frequency resources, the code hoppingmethod comprising: causing one or more groups, which use the samefrequency axis code and different time axis codes in a first slot, toconstitute one terminal group; and, when a time axis code length is lessthan a slot length, changing a terminal group according to the time axiscode length achieving orthogonality so that the one or more terminalsbelonging to the same terminal group in the first slot belong todifferent terminal groups in a second slot.

In accordance with another aspect of the present invention, there isprovided a terminal using code hopping in a wireless communicationsystem, the terminal apparatus comprising: a resource index receivingunit receiving a resource index that is changed according to a change ina slot or a symbol block; a frequency-axis code sequence allocating unitdetermining a frequency-axis code sequence according to the receivedresource index and allocating the determined frequency-axis codesequence to a terminal; and a time-axis code sequence allocating unitdetermining a time-axis code sequence according to the received resourceindex and allocating the determined time-axis code sequence to theterminal.

In accordance with another aspect of the present invention, there isprovided a base station using code hopping in a wireless communicationsystem, the base station comprising: a resource index transmitting unittransmitting a resource index that is changed according to a change in aslot or a symbol to terminals; a frequency-axis code sequencedetermining unit determining a frequency-axis code sequence according tothe resource index; and a time-axis code sequence determining unitdetermining a time-axis code sequence according to the resource index.

DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates time/frequency resources used by a terminal totransmit an uplink acknowledgement/negative acknowledgement (ACK/NACK)signal through a control channel in a 3^(rd) generation partnershipprojection long term evolution (3GPP LTE) system;

FIG. 2 illustrates a code sequence and a symbol transmitted to each ofsubcarriers in an ACK/NACK channel having the N subcarriers on afrequency axis and 7 orthogonal frequency division multiplexing (OFDM)symbols on a time axis;

FIG. 3 illustrates a slot structure of an ACK/NACK channel including 3reference signals per slot, according to an embodiment of the presentinvention;

FIG. 4 illustrates a slot structure of an ACK/NACK channel including 3reference signals per slot, according to another embodiment of thepresent invention;

FIG. 5 illustrates a slot structure of an ACK/NACK channel including 3reference signals per slot, according to another embodiment of thepresent invention;

FIG. 6 illustrates a frequency code hopping pattern of a terminal groupincluding one or more terminals in a first slot, according to anembodiment of the present invention;

FIG. 7 illustrates a frequency code hopping pattern of a terminal groupincluding one or more terminals in a second slot, according to anembodiment of the present invention;

FIG. 8 illustrates a frequency code hopping pattern of a terminal groupincluding one or more terminals in a first slot in the slot structure ofFIG. 5, according to an embodiment of the present invention;

FIG. 9 illustrates a frequency code hopping pattern of a terminal groupincluding one or more terminals in a second slot in the slot structureof FIG. 5, according to an embodiment of the present invention;

FIG. 10 is a block diagram of a terminal apparatus for mitigatinginterference between terminals in a wireless communication system usinga method of transmitting a signal, according to an embodiment of thepresent invention; and

FIG. 11 is a block diagram a base station employing a method oftransmitting a signal, according to an embodiment of the presentinvention

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In a wireless communication system, acknowledgement/negativeacknowledgement (ACK/NACK) control information sent by a terminal to abase station in order to signify that the terminal is successful orunsuccessful in demodulating data is transmitted and received. In orderto efficiently transmit and receive such ACK/NACK control information,the same ACK/NACK resources are used by a plurality of terminals,thereby causing interference between terminals in a cell or betweenterminals of adjacent cells. In order to mitigate the interference,there is a demand for efficient code hopping.

As described above, when acknowledgement/negative acknowledgement(ACK/NACK) control information sent by a terminal to a base station in awireless communication system is transmitted and received, the presentinvention can efficiently mitigate interference between terminals in acell or between terminals of adjacent cells which is caused when aplurality of terminals use the same ACK/NACK resources.

A code hopping method and apparatus for mitigating interference betweenterminals in a wireless communication system according to the presentinvention will now be described more fully with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown.

Detailed explanation will not be given when it is determined thatdetailed explanation about well-known functions and configurations ofthe present invention may dilute the point of the present invention.Terms used hereinafter are used considering the functions in the presentinvention and may be changed according to a user's or operatorsintention or usual practice. Accordingly, the terms will be definedbased on the entire content of the description of the present invention.

In particular, the term “frequency axis code” or “frequency axis codeindex” used hereinafter is interchangeable with “cyclic shift” or“cyclic shift index”, and the term “time axis code” or “time axis codeindex” used hereinafter is interchangeable with “orthogonal cover” or“orthogonal cover index”.

FIGS. 3 through 5 illustrate slot structures of acknowledgement/negativeacknowledgement (ACK/NACK) channels, each slot structure including 3reference signals per slot, according to embodiments of the presentinvention.

Referring to FIGS. 3 through 5, one slot includes 3 reference signalsand 4 control signals.

When a plurality of terminals are used, a receiver should be able toreceive and distinguish reference signals transmitted by the pluralityof terminals, and also should receive and distinguish control signalstransmitted by the plurality of terminals.

In order to distinguish signals, code division multiplexing (CDM) usingboth frequency and time resources may be used as described above.

In CDM, a time-axis sequence is an orthogonal sequence. When the numberof continuous orthogonal frequency division multiplexing (OFDM) symbolsalong a time axis is N_(t), a sequence length may be N_(t) and N_(t)sequences achieving orthogonality therebetween may be formed. When ani^(th) sequence is expressed as a row vector G_(i)=[C_(i,0), C_(1,1), .. . , C_(i), N_(t-1)], orthogonality is given by Equation (2).

$\begin{matrix}{{G_{i} \cdot G_{j}^{+}} = {{\lbrack {C_{i,0},C_{i,1},\ldots\mspace{14mu},C_{i,{N_{t} - 1}}} \rbrack \cdot \begin{bmatrix}C_{j,0}^{*} \\C_{j,1}^{*} \\\ldots \\\ldots \\C_{j,{N_{t} - 1}}^{*}\end{bmatrix}} = {{\sum\limits_{k = 0}^{N_{t} - 1}{C_{i,k}C_{j,k}^{*}}} = {N_{t}\delta_{i,j}}}}} & (2)\end{matrix}$

In Equation (2),

$\delta_{i,j} = \{ {\begin{matrix}{{1\mspace{14mu}{if}\mspace{14mu} i} = j} \\{{0\mspace{14mu}{if}\mspace{14mu} i} \neq j}\end{matrix}.} $

Theoretically, since the total number of resources on a frequency axisis M and there are 3 reference signals in FIGS. 3 through 5, M×3reference signals in total can be distinguished by CDM.

Since the total number of resources on the frequency axis is M and thereare 4 control signals in FIGS. 3 through 5, M×4 control signals can bedistinguished by CDM.

However, since each terminal should transmit at least one referencesignal in order for a base station to demodulate a control signal byusing the reference signal, the total number of distinguishableterminals is M×3. In this case, an orthogonal sequence having aspreading factor (SF) of 3 is used for the reference signals, and anorthogonal sequence having an SF of 4 is used for the control signals.

Code hopping for efficiently mitigating interference according to thepresent invention will now be explained. Code hopping is performed onboth or each of a frequency axis code and a time axis code.

(1) Code Hopping on Symbol Block-by-Symbol Block Basis

One frequency-axis code sequence and one time-axis code sequence areallocated to each terminal. It is assumed that a frequency axis code anda time axis code which are used by an i^(th) terminal in a t^(th) blockof an s^(th) slot are expressed as q_(i,t,s) and r_(i,s), respectively.In a multiplexing structure, 3 or less terminals in one symbol block usethe same frequency axis code and different time axis codes that aretransmitted through a plurality of blocks.

The present invention is not limited to the slot structures of FIGS. 3through 5, and the number of symbol blocks included in a slot may vary.

A Zadoff-Chu sequence of Equation 1 may be applied to a frequency axiscode. However, the frequency axis code is not limited to the Zadoff-Chusequence, and may use any sequence that achieves orthogonality.

At this time, a frequency axis code, which is used by a plurality ofterminals in the same cell, has the same primary index and differentcyclic delay indices. However, terminals belonging to different cellshave different primary indices.

A frequency axis code used by each terminal may be changed according toa block index “t”. It is assumed that a frequency axis code used by ani^(th) terminal for blocks belonging to an s^(th) slot is expressed as{q_(i,s,t=0), q_(i,s,t=1), q_(i,s,t=2), . . . , q_(i,s,t=7)}. A timeaxis code may be expressed as r_(i,s). If frequency axis codes used fora first symbol block by a j^(th) terminal and an i^(th) terminal are thesame, the same frequency axis code should be used for remaining symbolblocks. That is, when {q_(i,s,t=0)=q_(j,s,t=0), thenq_(i,s,t=k)=q_(j,s,t=k) (k=1, 2, 3, . . . , 6) should be satisfied. Thatis, frequency axis codes used by two terminals in all symbol blocksshould be the same. Also, if q_(i,s,t=k)≠q_(j,s,t=k), (then aq_(i,s,t=k)≠q_(j,s,t=k) (k=1, 2, 3, . . . , 6) should be satisfied. Thatis, frequency axis codes used by two terminals in all symbol blocks inthe same slot should be different from each other. The aforementionedcode hopping may be implemented as follows.

For starters, a terminal group is defined as follows. One terminal groupincludes one or more terminals that use the same frequency axis anddifferent orthogonal time axis codes. A plurality of terminals groupsare generated on a frequency axis, and one frequency code hoppingpattern corresponds to each of the plurality of terminal groups.

Since the one or more terminals belonging to the same terminal group usethe same frequency axis code even when blocks are changed, orthogonalityon a time axis between the terminals can be maintained.

If the terminals constituting the same terminal group are changed as asymbol block index is changed, orthogonality on a time axis between theterminals is broken, resulting in interference between the terminals.

FIG. 6 illustrate frequency code hopping patterns of terminal groupseach including one or more terminals in a first slot and a second slot,respectively, according to embodiments of the present invention.

Referring to FIG. 6, a terminal #0, a terminal #6, and a terminal #12constitute one terminal group. A frequency axis code commonly allocatedto the three terminals #0, #6, and #12 is changed as a symbol block ischanged. Accordingly, code hopping is carried out on a symbolblock-by-symbol block basis.

In other words, the terminals #0, #6, and #12 of the terminal group in afirst symbol block use the same frequency axis code but each terminaluses different time axis code. In a second symbol block, the terminals#0, #6, and #12 of the terminal group use a new frequency axis codedifferent from that in the first symbol block, thereby performing codehopping on a symbol block-by-symbol block basis.

(2) Code Hopping on Slot-by-Slot Basis

Code hopping performed on a slot-by-slot basis will now be explained.

An uplink ACK/NACK channel includes two slots. A plurality of terminalsignals are introduced through an ACK/NACK channel in code divisionmultiple access (CDMA). At this time, terminal speeds and powers aredifferent from one another. A terminal group is formed for each slot,and terminals belonging to the same terminal group in a first slotbelong to different terminal groups in a second slot in order tomitigate interference between the terminals, thereby improving receivingperformance.

Terminals in a terminal group are distinguishable by using differenttime axis codes as described above. For example, a specific terminal ina terminal group may have a high speed or high power because ofincomplete power control. Other terminals are interfered by thisspecific terminal. In particular, remaining terminals other than thespecific terminal in the same terminal group are most severelyinterfered by the specific terminal.

If constituent terminals of a terminal group are changed according to aslot such that terminals belonging to the same terminal group in a firstslot belong to different terminal groups in a second slot, interferencedue to the specific terminal may be mitigated.

Code hopping performed on a slot-by-slot basis will now be explainedwith reference to FIGS. 6 and 7 in further detail.

Referring to FIG. 6, the terminals #0, #6, and #12 constitute oneterminal group for each symbol block in the first slot. The terminals#0, #6, and #12 constituting one terminal group in FIG. 6 do not belongto the same terminal group in the second slot in FIG. 7.

Referring to FIG. 7, in the second slot, terminals #4, #10, and #0constitute a new terminal group. The terminals #6 and #12 constitutingthe same terminal group together with the terminal #0 in the first slotbelong to different terminal groups in the second slot. For example, theterminal #6 constitutes a new terminal group in the second slot togetherwith terminals that belong to different terminal groups in the firstslot. The rearrangement of terminals is performed by determining afrequency axis code and a time axis code according to resource indicescorresponding to each slot and changing terminals constituting aterminal group. A method of changing a time axis code will be explainedlater in detail.

Accordingly, terminals belonging to the same terminal group in the firstslot may not belong to the same terminal group in the second slot, andmay constitute a new terminal group together with other terminals.

The code hopping performed on the slot-by-slot basis can randomize andaverage interference between terminals. That is, since a terminal withhigh power in a first slot does not belong to the same terminal group ina second slot, interference can be mitigated.

The code hopping performed on the slot-by-slot basis may change a timeaxis code allocated to each terminal when a terminal group is changedaccording to slots. That is, a time axis code allocated to the terminal#0 in FIG. 6 and a time axis code allocated to the terminal #0 in FIG. 7may be different from each other.

FIGS. 8 and 9 illustrate frequency code hopping patterns of terminalgroups each including one or more terminals in a first slot and a secondslot, respectively, in the slot structure C of FIG. 5, according toembodiments of the present invention.

In this case, code hopping is independently performed for a referencesignal symbol block and a control signal symbol block. In FIGS. 8 and 9,it is assumed that a time axis code having a length of 4 is used forcontrol signal symbol blocks #0, #1, #5, and #6, whereas a time axiscode having a length of 3 is used for reference signal symbol blocks #2,#3, and #4. A terminal group used in a control signal symbol block and aterminal group used in a reference signal symbol block may be differentfrom each other as shown in FIGS. 8 and 9.

A terminal group defined in the control signal symbol blocks #0, #1, #5,and #6 in the first slot of FIG. 8 and a terminal group defined in thecontrol signal symbol blocks #0, #1, #5, and #6 in the second slot ofFIG. 9 are different from each other. Terminals constituting the sameterminal group together with the terminal #0 in the first slot belong toterminal groups different from that of the terminal #0 in the secondslot.

For example, while terminals #0, #6, and #12 constitute one terminalgroup in the first slot of FIG. 8, terminals #4, #0, and #16 constituteone terminal group in the second slot of FIG. 9. Accordingly, terminalsconstituting the same terminal group together with the terminal #0 inthe first slot belong to terminal groups different from that of theterminal #0 in the second slot.

A terminal group defined in the reference signal symbol blocks #2, #3,and #4 in the first slot of FIG. 8 is different from a terminal groupdefined in the reference signal symbol blocks #2, #3, and #4 in thesecond slot of FIG. 9. While terminals #0, #3, and #8 constitute aterminal group in the reference signal symbol block #2 in the first slotof FIG. 8, terminals #2, #0, and #13 constitute a terminal group in thereference signal symbol block #2 in the second slot of FIG. 9. That is,terminals constituting the same terminal group together with theterminal #0 in the first slot belong to terminal groups from that of theterminal #0 in the second slot.

When a terminal group is changed, a time axis code allocated to eachterminal may be changed. A time axis code allocated to the terminal #0in FIG. 8 and a time axis code allocated to the terminal #0 in FIG. 9may be different from each other. When a time axis code allocated to aterminal is changed whenever a terminal group is changed, interferencecaused by the use of a specific time axis code may be mitigated.

(3) Code Hopping Changing Terminal Group According to Time Axis CodeLength Basis

When a time axis code length does not occupy one slot, a terminal groupmay be changed according to a time axis code length basis. A method ofchanging a terminal group according to a time axis code length basis incode hopping will now be explained.

In the frequency code hopping patterns of FIGS. 3 through 5, when a timeaxis code length is 2, one time axis code is transmitted in two controlsignal symbol blocks C0 and C1, and another time axis code istransmitted in remaining control signal symbol blocks C2 and C3.

In this case, a terminal group is changed every 2 control signal symbolblocks. When a time axis code having a length of 3 is applied toreference signal symbol blocks R0, R1, and R2, a terminal group is notchanged in the reference signal symbol blocks R0, R1, and R2.

Whenever a terminal group is changed, a time axis code allocated to eachterminal may be changed. When a time axis code length of 2 is applied tothe control signal symbol blocks, C0, C1, C2, and C3, 4 time axis codesare transmitted for one terminal.

That is, a time axis code applied to the control signal symbol blocks C0and C1 of a first slot, a time axis code applied to the control signalsymbol blocks C2 and C3 of the first slot, a time axis code applied tothe control symbol blocks C0 and C1 of a second slot and a time axisapplied to the control signal symbol blocks C2 and C3 of the second slotare transmitted for one terminal. In this case, a terminal group ischanged three times, and a time axis code used by each terminal isaccordingly changed.

FIG. 10 is a block diagram of a terminal 1000 for mitigatinginterference between terminals in a wireless communication system usinga method of transmitting a signal, according to an embodiment of thepresent invention.

The terminal 1000 includes a resource index receiving unit 1010, afrequency-axis code sequence allocating unit 1020, and a time-axis codesequence allocating unit 1030. The resource index receiving unit 1010receives a resource index according to a change in a slot or a symbolblock. That is, a resource index is a basic value for determining afrequency-axis code sequence and a time-axis code sequence which are tobe determined according to a change from a first slot to a second slot.A terminal receives a resource index from a base station. The terminaland the base station share a frequency-axis code sequence and atime-axis code sequence allocated to the terminal on the basis of theresource index.

The frequency-axis code sequence allocating unit 1020 determines afrequency axis code to be used by a current slot on the basis of theresource index. The determined frequency axis code is allocated to aterminal. In code hopping performed on a symbol block-by-symbol blockbasis, a frequency axis code to be determined according to a symbolblock index that is changed whenever a symbol block is changed isdetermined and allocated to a terminal.

A plurality of terminals having the same frequency axis code in a firstslot receive a new resource index in a second slot, and accordingly havea new frequency axis code. Also, a plurality of terminals belonging toone terminal group have a time axis code in a second slot which isdifferent from a time axis code in a first slot. Accordingly, terminalsbelonging to the same terminal group in a first slot do not belong tothe same terminal group in a second slot, and constitute a new terminalgroup together with terminals belonging to different terminal groups inthe first slot. A terminal group may be changed on a symbolblock-by-symbol block basis in this way.

The time-axis code sequence allocating unit 1030 calculates a time-axiscode sequence to be allocated to terminals in a current slot or symbolblock on the basis of the resource index that is changed according tothe slot or the symbol block, and allocates the calculated time-axiscode sequence to the terminal.

In order to identify terminals, a base station should know theinformation of a code sequence allocated to each terminal. As describedabove, the base station transmits a resource index and shares atime-axis code sequence and a time-axis code sequence with each terminalby using the resource index. As a result, the base station knows afrequency axis code and a time axis code of each terminal in a slot orsymbol block.

The base station knows from a resource index in a first slot that aplurality of terminals have the same frequency axis code. The basestation also knows from a resource index in a second slot that terminalsbelonging to the same terminal group in the first slot do not belong tothe same terminal group, but have different frequency axis codes andbelong to different terminal groups in the second slot. The base stationshould also know that a time axis code may be changed according to aresource index in a slot.

As described above, a time axis code allocated to terminals in a firstslot is different from a time axis code allocated to the terminals in asecond slot.

A base station apparatus performing the aforesaid functions will now beexplained.

FIG. 11 is a block diagram illustrating a base station 1100 employing amethod of transmitting a signal, according to an embodiment of thepresent invention.

Referring to FIG. 11, the base station 1100 includes a resource indextransmitting unit 1110, a frequency-axis code sequence determining unit1120, and a time-axis code sequence determining unit 1130. The resourceindex transmitting unit 1110 transmits a resource index, which ischanged according to a change in a slot or a symbol block, to terminals.The frequency-axis code sequence determining unit 1120 determines afrequency-axis code sequence according to the resource index. Thetime-axis code sequence determining unit 1130 determines a time-axiscode sequence according to the resource index.

Code hopping according to the present invention may be embodied ascomputer-readable codes on a computer-readable recording medium. Thecomputer-readable recording medium is any data storage device that canstore data that can be thereafter read by a computer system. Examples ofthe computer-readable recording medium include read-only memories(ROMs), random-access memories (RAMs), CD-ROMs, magnetic tapes, floppydisks, optical data storage devices, and carrier waves (such as datatransmission through the Internet).

The computer-readable recording medium can also be distributed overnetwork coupled computer systems so that the compute readable code isstored and executed in a distributed fashion. Functional programs,codes, and code segments for embodying the present invention may beeasily deducted by programmers in the art to which the present inventionbelongs.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby one of ordinary skill in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims. Thepreferred embodiments should be considered in a descriptive sense onlyand not for purposes of limitation. Therefore, the scope of theinvention is defined not by the detailed description of the inventionbut by the appended claims, and all differences within the scope will beconstrued as being included in the present invention.

What is claimed is:
 1. A method of receiving an uplink signal by a basestation of a wireless communication system using a plurality of slots,each slot including a plurality of symbol blocks in a time domain, themethod comprising: determining a first code and a second code, the firstcode being hopped by a symbol block and a slot, and the second codebeing hopped by the slot; and receiving an uplink signal using the firstcode and the second code from a terminal, wherein the plurality ofsymbol blocks of each slot includes a first symbol block, a secondsymbol block, a third symbol block, a fourth symbol block, a fifthsymbol block, a sixth symbol block, and a seventh symbol block that aresequentially arranged in a time domain, wherein the first, second, sixthand seventh symbol blocks are used to carry a control signal, andwherein the third, fourth and fifth symbol blocks are used to carry areference signal.
 2. The method of claim 1, wherein the first codedetermines a cyclic shift of the uplink signal.
 3. The method of claim1, wherein the second code is an orthogonal cover of the uplink signal.4. The method of claim 1, wherein the uplink signal includes thereference signal, and wherein the second code uses an orthogonalsequence whose length is three.
 5. The method of claim 1, wherein theuplink signal includes the control signal of ACK/NAK, and wherein thesecond code uses an orthogonal sequence whose length is four.
 6. Amethod of transmitting an uplink signal by a terminal of a wirelesscommunication system using a plurality of slots, each slot including aplurality of symbol blocks in a time domain, the method comprising:determining a first code and a second code, the first code being hoppedby a symbol block and a slot, and the second code being hopped by theslot; and transmitting an uplink signal using the first code and thesecond code to a base station, wherein the plurality of symbol blocks ofeach slot includes a first symbol block, a second symbol block, a thirdsymbol block, a fourth symbol block, a fifth symbol block, a sixthsymbol block, and a seventh symbol block that are sequentially arrangedin the time domain, wherein the first, second, sixth and seventh symbolblocks are used to carry a control signal, and wherein the third, fourthand fifth symbol blocks are used to carry a reference signal.
 7. Themethod of claim 6, wherein the first code determines a cyclic shift ofthe uplink signal.
 8. The method of claim 6, wherein the second code isan orthogonal cover of the uplink signal.
 9. The method of claim 6,wherein the uplink signal includes the reference signal, and wherein thesecond code uses an orthogonal sequence whose length is three.
 10. Themethod of claim 6, wherein the uplink signal includes the control signalof ACK/NAK, and wherein the second code uses an orthogonal sequencewhose length is four.
 11. An apparatus for receiving an uplink signal ina wireless communication system using a plurality of slots, each slotincluding a plurality of symbol blocks in a time domain, the apparatuscomprising: a code sequence determining unit configured to determine afirst code and a second code, the first code being hopped by a symbolblock and a slot, and the second code being hopped by the slot; and areceiving unit configured to receive an uplink signal using the firstcode and the second code from a terminal, wherein the plurality ofsymbol blocks of each slot includes a first symbol block, a secondsymbol block, a third symbol block, a fourth symbol block, a fifthsymbol block, a sixth symbol block, and a seventh symbol block that aresequentially arranged in a time domain, wherein the first, second, sixthand seventh symbol blocks are used to carry a control signal, andwherein the third, fourth and fifth symbol blocks are used to carry areference signal.
 12. The apparatus of claim 11, wherein the first codedetermines a cyclic shift of the uplink signal.
 13. The apparatus ofclaim 11, wherein the second code is an orthogonal cover of the uplinksignal.
 14. The apparatus of claim 11, wherein the uplink signalincludes the reference signal, and wherein the second code uses anorthogonal sequence whose length is three.
 15. The apparatus of claim11, wherein the uplink signal includes the control signal of ACK/NAK,and wherein the second code uses an orthogonal sequence whose length isfour.
 16. An apparatus for transmitting an uplink signal in a wirelesscommunication system using a plurality of slots, each slot including aplurality of symbol blocks in a time domain, the method comprising: afirst unit configured to determine a first code and a second code, thefirst code being hopped by a symbol block and a slot, and the secondcode being hopped by the slot; and a second unit configured to transmitan uplink signal using the first code and the second code to a basestation, wherein the plurality of symbol blocks of each slot includes afirst symbol block, a second symbol block, a third symbol block, afourth symbol block, a fifth symbol block, a sixth symbol block, and aseventh symbol block that are sequentially arranged in the time domain,wherein the first, second, sixth and seventh symbol blocks are used tocarry a control signal, and wherein the third, fourth and fifth symbolblocks are used to carry a reference signal.
 17. The apparatus of claim16, wherein the first code determines a cyclic shift of the uplinksignal.
 18. The apparatus of claim 16, wherein the second code is anorthogonal cover of the uplink signal.
 19. The apparatus of claim 16,wherein the uplink signal includes the reference signal, and wherein thesecond code uses an orthogonal sequence whose length is three.
 20. Theapparatus of claim 16, wherein the uplink signal includes the controlsignal of ACK/NAK, and wherein the second code uses an orthogonalsequence whose length is four.